This invention relates to a system and method for registering location of a mobile terminal in a mobile communication system, more particularly, to a system and method for making an exchange office recognize a radio zone where the mobile terminal exists to control communication.
Conventionally, methods for making an exchange office control location of a mobile terminal that moves in a plurality of radio zones made up by a plurality of base stations are proposed, for example, one of them is disclosed in Japanese Patent Laid Open No. 71226 (1989).
In this method, a location display unit provided in an exchange office receives location information of a mobile terminal as well as a mobile terminal number and displays the location information of a mobile terminal. Then, location of the mobile terminal is recognized and controlled.
In this conventional location control method, as shown in FIG. 6 for example, a plurality of base stations B1 to B3 are connected with an exchange office A. The base stations make radio zones Z1 to Z3, respectively. A mobile terminal C receives one or more control signals from the base stations. If there are multiple control signals, the mobile terminal C registers its location to a base station having transmitted a control signal of which reception level is largest. According to this location registration, the exchange office A acquires location information of the mobile terminal via a base station having been registered the location. The location information acquired is displayed on the location display unit provided in the exchange office A.
In such a conventional method, when the mobile terminal moves to an area of a base station to which the mobile terminal registers its location overlapped with a neighboring radio zone from an area not overlapped with the neighboring radio zone, if a reception level of signal from the base station having been registered the location is more than a preset level, the mobile terminal does not register its location to the base station of the neighboring radio zone even if the reception level of signal from the neighboring base station is larger than the reception level of signal from the base station to which the mobile terminal registers its location. Therefore, the exchange office A can not recognize that the mobile terminal C has moved to the radio zone of neighboring base station.
To solve this problem, the mobile terminal compares reception levels from a plurality of base stations and register its location to a base station that transmits a signal of largest reception level in the area where radio zones overlap. In this method, the mobile terminal can register its location to the nearest base station, so the exchange office can properly control location of the mobile terminal.
However, in this method, if the mobile terminal is in an area where reception levels from neighboring base stations are nearly equal, the moving mobile terminal may frequently change the base station to be registered location. As a result, it may occur confusion on location control of the mobile terminal.